High-power LEDs (those LEDs that need a heat sink for normal operation) are the key components for solid-state lighting (SSL) products. The characteristics of high-power LEDs strongly depend on their operating temperatures. Junction temperature is the physical quantity for LEDs, universally reproducible, and known to be ideal parameter for testing LEDs, but it was difficult to measure. To ensure proper measurement and specifications of high-power LEDs, we have developed a new, practical method for measuring high-power LEDs in steady DC operation at any specified junction temperature. A temperature-controlled heat sink is used with electrical pulse measurements to set and control an LED at a specified junction temperature. The measurement of optical quantities can then be performed under conventional DC operating conditions with accurate, reproducible, and inter-comparable measurement results. This method bridges the gaps between pulse measurements done by the LED manufacturers and DC measurements done by the lighting industry. This method also enables the measurement of the thermal resistance of an LED between the junction and the heat sink surface at the same time as the optical quantities which is important knowledge for LED manufactures wanting to improve the design of LEDs and their thermal management system. This method has become basis for new standards on test methods for high power LEDs, being developed in IESNA and CIE (TC 2-63).
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